Patent GB-541511-A (GB)
Title: Improvements in photographic light sensitive materials
IPC: G03C1/035
Filed: 1940-04-15
Abstract: 541,511. Photographic light-sensitive material. KODAK, Ltd., DAVEY, E. P., and KNOTT, E. B. April 15, 1940, Nos. 6241/41, (divided out of 540,451), 14271/40 and 138/41. [Class 98 (ii)] Multi-contrast material comprises a single sensitive layer which comprises a mixture of two silver chloride emulsions (which contain at least 90 per cent silver chloride based on the total silver halide, but which may contain some silver iodide) of which one emulsion gives a gradation (measured at about the wavelength, including the range covering 40 Á on each side thereof, of the maximum speed of the emulsion concerned) less than 1.8 and the other emulsion gives a gradation of at least 2.5 greater, and of which one emulsion (A) is sensitized to have its maximum speed at least 60 Á further towards the long wavelengths than the maximum speed of the other emulsion (B), the speed of emulsion (A) measured at about the wavelength of maximum speed of (B) being not greater than half the speed of (B) measured at the same wavelengths, while measured at about the wave-length of maximum speed of (A), the speed of (A) is at least twice that of (B). The layer may comprise a mixture of non-optically sensitized silver chloride emulsion (including an emulsion sensitized in the blue region only and substantially insensitive beyond 430 Á) giving a gradation in the violet of between 0.8 and 1.8 (preferably 1.2 and 1.6) and a silver chloride emulsion optically sensitized in the region 430-570 Á and giving a gradation in the green-to-yellow of at least 2.5 (preferably 3.5) greater, the violet-speed of the non-optically sensitized emulsion being at least 1.8 (and preferably at least 2.5) times the violetspeed of the optically sensitized emulsion, while the green-to-yellow speed of the optically-sensitized emulsion is between 1/3 and 1“ (preferably ¥ and 1“) times the violet speed of the non- optically sensitized emulsion. Both emulsions may be optically sensitized, one in the region of 420-490 Á and giving a gradation in the blue between 0.8 and 1.8 (preferably between 1.2 and 1.6)' and the other in the region 500-570 Á and giving a gradation in the green-to-yellow of at least 2.5 (preferably 3.5) greater, the bluespeed of the first emulsion being at least twice (preferably at least 5 times) the blue-speed of the second, and between “ and 4 times the yellowspeed of the second. The emulsions are preferably each substantially insensitive at the wavelength of maximum sensitivity of the other. Both emulsions may have a violet-speed which is not more than 1/10 the blue- and the yellowspeeds. The emulsions may have substantially no sensitivity at wavelengths beyond 600 Á. Suitable exposure-filters for use in obtaining the various contrasts are referred to. Where the optically sensitized emulsion has a maximum in the region 500-590 Á, this should be the one giving the higher gradation. The speeds of the two emulsions should be about the same in the spectral regions used for exposure. With an opaque support, such as white paper, density measurement are made with reflected light. A formula for a standard developing solution is given. The emulsion giving the lower gradation should be one having a characteristic H and D curve whose straight portion is as long as possible. One or more sensitizing dyes may be used for the optically sensitized emulsion or emulsions, and such dyes are incorporated before mixing the emulsions, and in such a manner, as for example described in Specification 540,451, that the tendency of the dye or dyes to wander is avoided or minimized. The material may be made with a greater gradation difference than necessary to compensate for loss due to dyewandering. An emulsion may be sensitized to a maximum near 470 Á by 3-ethyl-5-(1-methyl- 2-#-naphthoxazolylidene-rhodanine or the corresponding 3-n-heptyl compound. Dye-wandering may also be reduced by the incorporation in one or both of the emulsions of a small amount, e.g. about 1 per cent, of silver bromide, preferably in the emulsion giving the lower gradation. The minimum amount of sensitizing dye is employed, and after incorporation the emulsion is kept at an elevated temperature for as long as conveniently possible and then cooled to 30‹C before mixing. The dye may be incorporated at an early stage in the preparation of the emulsion, and at some later stage the emulsion is kept at about 45‹ C for about half-hour at a pH below 7, citric or hydrochloric acid being added to adjust the pH. In example (1), to an amount of silver chloride emulsion made from 200 grams of silver nitrate is added, immediately after formation of the silver chloride, 0.01 gram of the dye of example 3 of Specification 532,098, and the emulsion is ripened and more gelatine added. The emulsion has a violet-speed of 0.06, a greento yellow of 0.3 and a gradation in the greento-yellow of 5.0. This is mixed at 30‹ C with an equal amount of a non-optically sensitized silver chloride emulsion containing 3 per cent of silver bromide and 1 per cent of silver iodide and having a violet-speed of 0.3 and a gradation of 1.5, and the mixture is coated. In example (2), the first emulsion is prepared similarly to the sensitized emulsion of example (1), and has a violet-speed of 0.1, a green-to-yellow speed of 0.8, and a gradation in the green-to-yellow of 5.0. A sensitized silver chloride emulsion is similarly prepared using the dye 3-n-heptyl-5-(1- methyl-2-#-na phthoxazolylidene )-rhodanine, and has a violet-speed of 0.3, a blue speed of 1.1, and a gradation in the blue of 1.4. The two emulsions are mixed in equal proportions at 30 ‹C and coated. An emulsion sensitized to have a maximum in the blue may be mixed with a non-optically sensitized emulsion with a maximum in the violet, either (preferably the sensitized one) giving the higher gradation. More than two emulsions may be mixed. Specifications 15045/12, [Class 98 (ii)], 450,958, 524,552, 532,098 and 540,464 are referred to.